Major Landmasses on Pangea - Map Quiz

As I understand it, and I could be wrong. The continents represent the bulk of the land as they do now. They were all conjoined at this point, but moving apart.

As they move apart, it isn't a case of like moving two boxes apart in a sink, the water doesn't just rush in to fill a huge gap. This happens over a LONG period of time. The ground may crack a little and a valley open up, rivers and lakes form. The sea constantly wears down where the rives flow into it, and as sea levels rise, floodplains are formed.

It's not until the continents are substantially apart that these intermediate lands begin to split and fall away. And when each one goes it is catastrophic, like the fall of Doggerland here in the UK. Where the biggest islands are right now are the remnants of that pulling apart. I could be wrong but that's how I understand it.

TLDR it takes a long time to split and those bits aren't flooded yet.

Thanks @Stewart and @zephyr! Makes sense. So similar to the Great Rift Valley in Africa I guess? I've heard before that East Africa may become a separate continent in the future using a similar process.